octeontx2-af: Priority flow control configuration support

Prirority based flow control (802.1Qbb)  mechanism is similar to
ethernet pause frames (802.3x) instead pausing all traffic on a link,
PFC allows user to selectively pause traffic according to its class.

Oceteontx2 MAC block (CGX) and CN10K Mac block (RPM) both supports
PFC. As upper layer mbox handler is same for both the MACs, this
patch configures PFC by calling apporopritate callbacks.

Signed-off-by: Sunil Kumar Kori <skori@marvell.com>
Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Signed-off-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>